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The presidential campaigns will now focus on the nearly two dozen states holding primaries or caucuses on Feb. 5. These "Super Tuesday" states pose unique strategic challenges as the candidates scramble for votes in some unlikely places. They'll have to navigate a complex process of choosing delegates that varies from state to state.

The big states up for grabs include California (170 Republican/370 Democrat), New York (101/232), Georgia (72/87), Illinois (57/153) and New Jersey (52/107).

But don't bother staying up late for the California results. The state recently switched to optical scan ballots in some counties, which could lead to delays in counting votes.

In general

Republicans award delegates based on a winner-take-all approach within congressional districts or statewide. That means a GOP candidate could win most -- or even all -- of the delegates in a state where he is strong. Likewise, a candidate could narrowly finish second and come away empty-handed.

Democrats award delegates based on a proportional vote in congressional districts or statewide. That means a candidate who wins 25 percent of the vote could expect to receive roughly 25 percent of the delegates in a congressional district or state. But it also means that in a 51-49 finish, each candidate might get the same number of delegates.

Who's ahead

We don't have recent polls in every state (pollsters have focused on the big ones), but here's an overview of where the candidates are strong based on available polling:

Republicans: John McCain has gained ground in the past few weeks and now has the lead in national polls, as well as in California and New York. Mitt Romney is second in many polls but still within striking distance. Mike Huckabee is stronger in Southern states and has the lead in Georgia.

Democrats: Hillary Clinton leads in several key Super Tuesday states such as California, New Jersey and her home state of New York, but a Gallup national tracking poll shows Barack Obama steadily chipping away at her lead.The strategy

Think big: Some candidates will go after the jackpots -states such as California and New York that have large media markets and offer the most delegates.

Cherry-picking: Others will try to cherry-pick states or even congressional districts where they could pick up delegates. That's why Obama is campaigning in Kansas (32 delegates) and Idaho (18).

Friendly turf: Some candidates will aim for favorable regions. Romney is expected to be stronger in the Northeast (where four states have primaries), while Huckabee will target Southern states (also four states)that have more Christian conservative voters.

One more thing

Political analyst Stuart Rothenberg: "I think you'd want to be very cold-blooded ... you do this on the basis of where you get the most delegates."